Since the advent of sliding windows and doors, such as glass patio doors, attempts have been made to provide locking means for such windows and doors. While adequate means have long since been available for securely locking windows and doors in the closed position, the numerous devices proposed for locking windows and doors while in the partially open position have never been successful.
It has long been recognized that a need exists for a means for locking sliding doors and windows in a partially open position, so as to prevent intruders from opening the window or door wider to gain access. Resort has been had to poles or sticks of wood to be lodged between the window sash and the frame. Such means have proven partially effective for laterally-sliding windows and doors, but are ineffective for vertically sliding windows.
Several prior art attempts at other types of locks have been patented, such as those disclosed in U.S. Pat. Nos.: 1,100,820; 1,442,657; 1,461,467; 1,311,052; 1,398,174; and 3,428,349. The 1,311,052 and 1,398,174 patents appear to disclose means for wedging a semi-circular-shaped rotatable member against a window frame, but rely on a toothed surface on the member to engage the frame and prevent further rotation of the member.
In practice these prior art devices are not effective. The toothed edge of the rotating member chews into the normally wooden frame of the window and present unsightly appearance. Moreover, over a period of time a channel is gouged into the frame and the member cannot engage the frame. A Major inadequacy of all of the pressure-type locks results from the normal spacing between the edge of the sash and the window frame. When a pressure-type lock of the prior art is engaged with a window frame, the window itself is shifted over to occupy the space between the opposite sash and the frame, thereby preventing a secure engagement of the rotatable member with the frame.
It is therefore an object of this invention to provide a sliding window and door locking means which will enable the window or door to be secured in any open position, and will permit the window or door to be closed, but not opened further from the exterior.
It is also an object of this invention to provide a locking means for both laterally and vertically sliding windows and doors.
It is a further object of this invention to provide a locking means which permits positive engagement of cam means without lateral slippage of the window or overriding of the cam means.